Method for producing caoutchouc particles

Details Method for producing caoutchouc particles Method for producing caoutchouc particles

2002-09-10

2004-04-20

Egwim, Kelechi C. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S814000, C524S821000, C524S836000, C525S242000, C525S244000, C525S313000, C525S902000, C526S201000, C526S295000, C526S335000, C526S337000, C526S338000, C526S339000, C526S340000, C526S340100

Reexamination Certificate

active

06723774

ABSTRACT:

The invention relates to a process for preparing rubber particles K comprising in polymerized form
A) from 80 to 100% by weight, based on K, of one or more conjugated diene monomers A, and
B) from 0 to 20% by weight, based on K, of one or more monoethylenically unsaturated comonomers B
by emulsion polymerization in the presence of an emulsifier and a polymerization initiator. The invention further relates to the rubber particles K prepared by the process and to their use as a constituent of thermoplastic molding compounds, dispersions, paper coating compositions and surface coatings, and for textile finishing.
Processes for the emulsion polymerization of rubbers based on butadiene or other rubber-forming dienes where some or all of the monomers are metered in during the polymerization (known as feed techniques) are known.
For instance, DE-A 34 47 585 describes styrene-butadiene latices whose graft base contains at least 86% by weight styrene and whose graft contains at least 62% by weight styrene, which are prepared by a feed technique with or without a polystyrene seed latex. This document does not disclose butadiene-rich latices.
EP-A 387 855 discloses a feed technique for preparing polymer particles comprising, inter alia, styrene and butadiene where a seed latex having a weight-average molecular mass {overscore (M)}
w
of only from 500 to 10,000 is used. Although the comparative examples do include seed latices of relatively high molecular mass, the butadiene fraction in the feed stream is not more than 40% by weight, i.e., these polymer particles are also low in butadiene.
EP-A 814 103 discloses a feed technique for preparing polymer dispersions comprising, inter alia, styrene and butadiene where a seed latex is mixed with the monomers and emulsified and this emulsion is then metered into the heated polymerization reactor. The seed latex, accordingly, is not included in the initial charge but instead is present in the feed stream, leading to an undesirably wide particle size distribution.
EP-A 276 894 discloses adhesive compositions comprising starch and styrene-butadiene latices. The latices are prepared by a feed technique using a polystyrene seed latex and contain more than 60% by weight styrene, and are therefore low in butadiene.
EP-A 792 891 discloses a process for preparing latices based on conjugated dienes such as butadiene, where a seed latex, comprising, in particular, polystyrene particles of from 10 to 80 nm in diameter, is included in the initial charge. In the presence of an activator (i.e. initiator) and an emulsifier, the entirety of the monomers are metered in such that a defined relationship between polymerization rate and monomer addition rate is established. The polymerization is only ended when the conversion is at least 95%. Accordingly, only the seed latex is included in the initial charge, and not a portion of the monomers. In comparative experiments, all monomers are introduced in the initial charge together with the seed latex (batch, i.e., no feed stream).
EP-A 761 693 discloses a process for preparing diene latices where a certain fraction of the reaction mixture is included in the initial charge, so that a defined vessel filling level is achieved, and the remainder of the reaction mixture is run in under controlled conditions. Using this process it is possible to produce only small particles of from 60 to 120 nm in diameter. The increased utilization of the gas space in the vessel for cooling purposes, which is intrinsic to the process, leads to increased formation of coagulum. Moreover, the polymerization time is uneconomically long.
The latices and polymer particles of the prior art have the following disadvantages: they are low in butadiene, or long polymerization times are needed in order to prepare relatively large particles. Moreover, the prior art processes have large amounts of unreacted monomers during the polymerization reaction (known as hold-up), which may be a safety risk in the case of disruptions (poor operational safety).
It is an object of the present invention to provide a process which does not have the disadvantages depicted. In particular, the intention was to provide a process which enables diene-rich rubber particles having diene contents ≧80% by weight and particle sizes above 100 nm to be prepared in a short time. Furthermore, the process is to be operationally safe by virtue of the fact that the proportion of unreacted monomers (hold-up) in the reactor is kept low.
We have found that this object is achieved by the process defined at the outset. This process comprises
1) initially introducing a mixture M
1
comprising, based on M
1
,
M
1
a
) from 20 to 100% by weight of the water needed to prepare the emulsion (emulsion water), and
M
1
b
) from 0.1 to 100% by weight of the emulsifier,
2) simultaneously or subsequently adding a mixture M
2
comprising, based on M
2
,
M
2
a
) from 90 to 100% by weight of one or more monomers selected from styrene, &agr;-methylstyrene, butadiene, n-butyl acrylate, methyl methacrylate and acrylonitrile, and
M
2
b
) from 0 to 10% by weight of one or more copolymerizable monomers,
the monomers M
2
a
) and M
2
b
) being added alternatively in polymerized form as a seed latex, or in monomeric form with subsequent in situ polymerization to give a seed latex, or as a mixture of polymerized and monomeric form, and the seed latex polymer having a weight-average molecular mass of more than 20,000,
3) then starting the polymerization of the resulting mixture in the presence of the polymerization initiator at temperatures of from 5 to 95° C.,
4) simultaneously or subsequently adding a mixture M
3
comprising
M
3
a
) from 0 to 100% by weight, based on B, of the comonomers B, and
M
3
b
) from 0 to 25% by weight, based on A, of the diene monomers A,
5) simultaneously or subsequently metering in a mixture M
4
comprising
M
4
a
) the remaining 75 to 100% by weight, based on A, of the diene monomers A, and
M
4
b
) the remaining 0 to 100% by weight, based on B, of the comonomers B,
and carrying out polymerization, and
6) subsequently ending the polymerization at a conversion above 90 and below 95%, based on the sum of the monomers,
the remaining 0 to 80% by weight of the emulsion water and the remaining 0 to 99.9% by weight of the emulsifier being added individually or separately from one another in one or more of steps 2) to 5).
We have additionally found the rubber particles K prepared by the process and their uses as specified at the outset.
The rubber particles K prepared by the process of the invention comprise in polymerized form
A) from 80 to 100, preferably from 85 to 100% by weight, based on K, of one or more conjugated diene monomers A, and
B) from 0 to 20, preferably from 0 to 15% by weight, based on K, of one or more monoethylenically unsaturated comonomers B which are copolymerizable with the diene monomers A to give copolymers.
Suitable diene monomers A are all dienes having conjugated double bonds, especially butadiene, isoprene, chloroprene or mixtures thereof. Particular preference is given to butadiene or isoprene or mixtures thereof. With very particular preference, butadiene is used.
Suitable comonomers B are all monoethylenically unsaturated monomers, especially
vinylaromatic monomers such as styrene, styrene derivatives of the formula I
where R
1
and R
2
are hydrogen or C
1
-C
8
-alkyl and n is 0, 1, 2 or 3;
methacrylonitrile, acrylonitrile;
acrylic acid, methacrylic acid, and also dicarboxylic acids such as maleic acid and fumaric acid and also their anhydrides such as maleic anhydride;
nitrogen-functional monomers such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, vinylimidazole, vinylpyrrolidone, vinylcaprolactam, vinylcarbazole, vinylaniline, acrylamide;
C
1
-C
10
alkyl esters of acrylic acid, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, ethylhexyl acrylate, and the corresponding C
1
-C
10
alkyl esters of methacrylic acid, and also hydroxyethyl acr

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